Thus far, the highest output power measured on GaN-based lasers is about 7W, as shown in the picture.  In comparison, some GaAs-based lasers emit more than 30W in continuous-wave operation at room temperature. A key reason for this difference is the inherently large p-side electrical resistance of GaN-based laser diodes. It leads to strong Joule heating which lowers the gain and boosts various loss mechanisms that eventually cause the typical power roll-off at high currents.  Read more of this post
Energy band diagram (red) and light emission profile (blue) of the proposed LED design.
Quantum efficiency is the ratio of emitted photons to injected electrons. So, how can an electron generate more than one photon ? One possible solution was demonstrated numerically by inserting tunnel junctions into the multi-quantum well (MQW) active region of a GaN-based LED (details). With one tunnel-junction (TJ), each electron gets two chances to generate a photon, because it can tunnel back into the conduction band after the first generation process. Inspired by the numerical demonstration, such GaN-based TJ-MQW LED was recently fabricated for the first time (details). With three tunnel-junctions (picture), each electron gets four chances to generate a photon, enabling quantum efficiencies up to 400%. Read more of this post